1. Field of the Invention
The present invention generally relates to computer-aided design and, more particularly, to a method for managing annotations in a computer-aided design drawing.
2. Description of the Related Art
The term computer-aided design (CAD) generally refers to a broad variety of computer-based tools used by architects, engineers, and other construction and design professionals. CAD applications may be used to construct computer models representing virtually any real-world object, e.g., a machine part, a bicycle, a house, a skyscraper, or a stretch of highway complete with bridges and buried utilities.
Most CAD applications provide an environment for creating models at their real world size. This environment is typically called model space. In model space, everything exists as in the real world, and the model provides a 1:1 scale representation of the real-world objects. If a building is 80 feet by 40 feet, it is created at that size.
Since the model or portions thereof need to be annotated and output to a sheet of paper, CAD applications often have an environment for composing different views of the model along with annotations that document the model. This environment is known as paper space. In paper space, the sheet of paper is represented in 1:1 scale, and the information contained in model space is presented in paper space by way of one or more viewports that can be scaled, rotated, and arranged in different ways to create the final drawing to be printed or plotted.
Viewports in paper space are simply bounded views into the model. In order to display a large model on a sheet of paper, viewports can be assigned a viewport scale.
The display of the model is scaled so that it can be seen on the sheet at the desired size, e.g., ¼″=1′-0″ or 1:100, 2:1, etc. Different parts of the model may be displayed in different viewports in paper scale at different scales. The sheet (paper space) is generally plotted at scale of 1:1.
While users like to design models at their real-word size, they need to create their annotations at a size that is appropriate for the sheet. Annotations may be created in the paper space environment or in the model space environment. In conventional CAD applications, when the text, dimensions, symbols, and other annotations are drawn in model space (the same environment as the model geometry), these annotations along with the model geometry are scaled down when displayed in a viewport in paper space. The size of such text, dimensions, symbols, and other annotations has to be carefully selected so that they will scale correctly to give the desired appearance in the final printouts and plots that will be generated from paper space. For example, if drawing sheets of a model are to be plotted with the model scaled at 1:100, and the user wants the plotted text size to be ⅛″, the text must be drawn 100/8″ in model space.
When working with a few viewports in paper space or with a single paper space scale, the planning that is required for correct annotation scaling may be manageable. However, when the same geometry and annotations need to be plotted multiple times at different scales, the user has to create duplicate annotations on different layers, in different positions, and adjust the visibility of each layer to create the desired effect. This, of course, not only takes a significant amount of time, but results in potential out-of-sync problems, making the drawing environment more complex and difficult to manage.